16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
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DTC-SVPWM OF INDUCTION MOTOR DRIVE WITH THREE LEVEL
H-BRIDGES INVERTER
Jagan Mohana Rao MALLA
Siva Ganesh MALLA
Asst.prof. dept of AE&IE, GIET Gunupur, Orissa, India.
E-Mail: malla_papers@yahoo.com
Vignan’s engineering college, Guntur, Andhra Pradesh
E-Mail: malla_46@yahoo.co.in
Abstract: Direct Torque Control is a control technique used
in AC drive systems to obtain high performance torque
control. The conventional DTC drive contains a pair of
hysteresis comparators, a flux and torque estimator and a
voltage vector selection table. The torque and flux are
controlled simultaneously by applying suitable voltage
vectors, and by limiting these quantities within their
hysteresis bands, de-coupled control of torque and flux can
be achieved. However, as with other hysteresis-bases
systems, DTC drives utilizing hysteresis comparators suffer
from high torque ripple and variable switching frequency.
typically aligned to the rotor flux. In this reference
frame, the torque and flux producing components of the
stator current are decoupled. A PI controller is then used
to regulate the output voltage to achieve the reputed
stator current and therefore torque. This PI controller
limits the transient response of the torque controller.
The most common solution to this problem is to use the space
vector with multilevel inverter depends on the reference
torque and flux. The reference voltage vector is then realized
using a voltage vector modulator. Several variations of
DTC-SVM with multilevel inverter have been proposed and
discussed in the literature. The work of this project is to
study, evaluate and compare the various techniques of the
DTC-SVM with parallel inverter applied to the induction
machines through simulations. The simulations were carried
out using MATLAB/SIMULINK simulation package.
Evaluation was made based on the drive performance, which
includes dynamic torque and flux responses, feasibility and
the complexity of the systems. It is better technology for
electric vehicles.
Key words: Multilevel inverter, DTC-SVM, converter, electric
vehicles, reliability, SVPWM, 3 level H-Bridge inverter.
1. INTRODUCTION
Multilevel inverters have been developed to
overcome harmonics in output, and improve the shape of
output to reach sinusoidal waveform. By using PWM
inverters have been developed to overcome
shortcomings in solid-state switching device ratings.
Direct Torque Control (DTC) uses an induction
motor model to achieve a desired output torque. By
using only current and voltage measurements, it is
possible to estimate the instantaneous stator flux and
output torque. An induction motor model is then used to
predict the voltage required to drive the flux and torque
to demanded values within a fixed time period. This
calculated voltage is then synthesized using space vector
modulation (SVM).
The stator flux vector, and the torque produced by
the motor, Tem , can be estimated using and
respectively. These only require knowledge of the
previously applied voltage vector, measured stator
current, and stator resistance.
As shown in Fig 1, the voltage required to drive the
error in the torque and flux to zero is calculated directly.
The calculated voltage is then synthesized using Space
Vector Modulation. If the inverter is not capable of
generating the required voltage then the voltage vector
which will drive the torque and flux towards the demand
value is chosen and held for the complete cycle.
In this paper we give detail model of multilevel
inverter applications in ac drives and give DTC-SVM of
induction motor with three level H-Bridge inverter and
their results are compare with classical model or DTCSVM of induction motor with simple inverter.
2. MULTILEVEL INVERTER FOR DTC-SVM OF
INDUCTION MOTOR
Induction motor torque control has traditionally been
achieved using Field Oriented Control (FOC). This
involves the transformation of stator currents into
asynchronously rotating d-q reference frame that is
Fig1. DTC-SVM of IM drive with 3level inverter.
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
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Fig 5 pulse generation for three level H- Bridge inverter
Fig 2 Basic DTC induction motor scheme
3. SIMULATION RESULTS
Fig 3 System diagram of PSSVM-DTC
Fig 4: space vector modulation for 3 level inverter
Fig. 6.a diagram of general DTC and fig 6.b diagram of
DTC-SVM with three level H-Bridge inverter using
SIMULINK/MATLAB
Fig. 7 (a) and (b) show the simulation results for load
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
744
stator currents for general and DTC-SVM with three
level H-Bridge nverter respectively for a reference speed
of 1440 rpm. As shown, reduces steady-state ripple in
stator current.
Fig (b)
Fig. 8 Simulation results for flux response of (a) general
DTC (b) DTC-SVM with three level H-Bridge inverter
for 1440 rpm.
Fig (a)
Fig.9 (a) and (b) show the 3-phase stator current for
general and DTC-SVM with three level H-Bridge
inverter respectively for a reference speed of 1440 rpm.
An on load torque applied at 2 second. The enlarged
view of Fig.9 (a) and (b) at a torque load condition is
presented. The proposed method (DTC-SVM with three
level inverter) is able to reduce ripples in 3-phase stator
current as well.
Fig (b)
Fig. 7 Simulation results for stator current of (a) general
DTC (b) DTC-SVM with three level H-Bridge inverter
for 1440 rpm
Fig. 8 (a) and (b) show the stator flux response for
general and DTC-SVM with three level H-Bridge
inverter respectively for a reference speed of 1440 rpm.
The classical DTC uses a constant flux command of
0.742 Wb, whereas SVM method uses an optimized
value, which 0.989 Wb. The SVM method reduces the
flux ripple to a considerable lower mount.
Fig (a)
Fig (b)
Fig. 9 Simulation results for stator current of (a) general
DTC (b) DTC-SVM with three level H-Bridge inverter
for 1440 rpm.
Fig (a)
Fig.10 (a) and (b) Show the speed for general and
DTC-SVM with three level H-Bridge inverter
respectively for a reference speed of 1440 rpm. It is
observed that, the transient and steady state ripples are
less in DTC-SVM.
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
745
Fig (a)
Fig. 11 Simulation results for 3-phase voltages of ((a)
general DTC (b) DTC-SVM with three level H-Bridge
inverter for 1440 rpm.
Fig(b)
Fig. 10 Simulation results for Speed of (a) general DTC
(b) DTC-SVM with three level H-Bridge inverter for
1440 rpm.
Fig. 12 (a) and (b) show stator flux trajectory for
general and DTC-SVM with three level H-Bridge
inverter respectively for a reference speed of 1440 rpm.
The smoother flux trajectory for the proposed one
confirms the ripple reduction in torque, flux, stator
current and speed response.
Fig.11 (a) and (b) Show the 3-phase output voltages
for general and DTC-SVM with three level H-Bridge
inverter respectively for a reference speed of 1440 rpm.
It is observed that, in on load condition the output
voltage ripples are reduced in DTC-SVM
Fig (a)
Fig(a)
Fig (b)
Fig. 12 (c) and (d) show electric torque response for
general and DTC-SVM with three level H-Bridge
inverter respectively a reference speed of 1440 rpm. A
step change in load torque from 20 N-m to 5 N-m is
applied at 1.5 second. In addition to the inherent
disadvantages of general DTC, the constant reference
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
746
flux causes higher ripple at lower torque level. The
proposed (DTC-SVM with three level H-Bridge) method
causes lower ripple at lower torque level. In addition to
the torque ripple minimization (~1/12th), this method is
also able to eliminate the torque under-shoot and overshoots.
Torque (N-m)
30
20
10
0
-10
1.0
1.25
1.5
Time (Sec)
1.75
2.0
Fig (c)
Torque (N-m)
30
Fig 14.2: line voltage of 3 level inverter (mi=1; mf=21;
Ar=1).
20
10
4 CONCLUSION
This technology is better for multilevel inverter from
construction and life time point of view, and also low
THD values.
0
-10
1.0
1.25
1.50
Time (Sec)
1.75
2.0
Fig (d)
Fig. 13 Simulation results for torque response of (a) &
(c) general DTC, (b) & (d) DTC-SVM with 3 level HBridge inverter for 1440 rpm.
3- Level H-Bridge inverter
Fig 14.1: phase voltage of 3 level inverter (mi=1; mf=21;
Ar=1). THD is 49.46%
This paper has proposed a DTC-SVM control
method with a three-level inverter for induction motor. It
operates the three-level inverter effectively as a twolevel inverter. This allows for a significant reduction in
the rating requirements of the clamping diodes, which
would result in a lower cost implementation of this
topology. The paper also extends the parallel topology to
the use of a charge pump circuit as a method to obtain
the required independently referenced gate drive power
supplies. This charge pump circuit eliminates the need
for individual power transformers for each of the gate
drive supplies which significantly reduces the cost and
size of these required supplies. With these proposed
methods, a low power motor drive was constructed using
inexpensive high-volume low-voltage power MOSFETs
and other low cost discrete components. Thus the paper
demonstrates the possibility of basing a low power
motor drive around inexpensive power MOSFET
switches that previously could not be used due to voltage
limitations. While the proposed converter was
constructed using discrete power devices, it should be
noted that the two-level control principle and four-level
charge pump make this topology attractive for
integration into a single device package much like a
standard six-pack arrangement. With the lower voltage
rating requirement of the main switches, and the familiar
and standard two-level control principles, this topology
could become even more economical than a standard
two-level inverter depending on what future device dies
are developed and manufactured. This is important since
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.
16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010
the trend of integration into standard packages and
automated manufacturing focus attention on
performance and total cost while making the actual
topology inside the package of lesser importance.
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Jagan Mohana Rao Malla was born on
1977
in
Nagulapalli,
Anakapalli,
Visakhapatnam, Andhra Pradesh, India.
Present he is working as asst. professor. in
Deportment of AE&IE, GIET College
Gunupur, Orissa, India. He received the B.E
from S.R.K.R engineering college affiliated
to Andhra University, Visakhapatnam,
Andhra Pradesh and M.Tech from J.N.T.U Hyderabad.
Siva Ganesh Malla was born on 1986 in
Nagulapalli, Anakapalli, Visakhapatnam,
Andhra Pradesh, India. He received the
B.Tech in Electrical Deportment from
Jawaharlal Nehru Technological University
Hyderabad in 2007 and M.Tech in Power
Electronics and Electric Drives in Electrical
Deportment from Jawaharlal Nehru
Technological University Kakinada in 2009.
Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.